Mercurial > imath

changeset 2:5ab4f6048553 draft

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Fix the for loop in atan
author Radomir Dopieralski <sheep-devel@sheep.art.pl>
date Wed, 21 Dec 2016 23:43:10 +0100
parents a56bbe3b03df
children 230eac2a984f
files imath.c
diffstat 1 files changed, 12 insertions(+), 12 deletions(-) [+]
line wrap: on
line diff
--- a/imath.c	Wed Dec 21 22:28:44 2016 +0100
+++ b/imath.c	Wed Dec 21 23:43:10 2016 +0100
@@ -31,7 +31,6 @@
 int16_t iatan2(int16_t y, int16_t x) {
     int16_t result = 0;
     uint16_t tx, ux, uy;
-    uint8_t i = 0;
 
     if (x == 0 && y == 0) {
         return 0;
@@ -54,7 +53,7 @@
         ux <<= 1;
         uy <<= 1;
     }
-    while (i < ITERATIONS) {
+    for (uint8_t i = 0; i < ITERATIONS; ++i) {
         if (uy > ux >> i) {
             tx = ux;
             ux += uy >> i;
@@ -62,7 +61,7 @@
             result += pgm_read_word(&ATAN[i]);
         }
     }
-    return result + (pgm_read_word(&ATAN[i - 1]) >> 1);
+    return result + (pgm_read_word(&ATAN[ITERATIONS - 1]) >> 1);
 }
 
 /*
@@ -73,20 +72,21 @@
     int16_t result = 0;
     int16_t x = SCALE;
     int16_t y = 0;
-    int16_t tx;
+    int16_t dx, dy, dr;
 
     for (uint8_t i = 0; i < ITERATIONS; ++i) {
         for (uint8_t j = 0; j < 2; ++j) {
-            tx = x;
+            dx = y >> i;
+            dy = -(x >> i);
+            dr = -pgm_read_word(&ATAN[i]);
             if (y < value) {
-                x -= y >> i;
-                y += tx >> i;
-                result += pgm_read_word(&ATAN[i]);
-            } else {
-                x += y >> i;
-                y -= tx >> i;
-                result -= pgm_read_word(&ATAN[i]);
+                dx = -dx;
+                dy = -dy;
+                dr = -dr;
             }
+            x += dx;
+            y += dy;
+            result += dr;
         }
         value += value >> (i << 1);
     }